The relationships among equilibrium insulin binding, glucose transport activity, and glucose metabolism have been examined in isolated adipose cells of widely varying size prepared from genetically obese Zucker Fatty rats and their lean controls of widely varying age and body weight. Preliminary results suggest that increasing age and body weight within the control animals are accompanied by increasing adipose cell size; increasing insulin binding; increasing basal, but decreasing insulin-stimulated, total glucose utilization. Roughly similar relationships are observed with increasing age and body weight within the genetically obese animals except for insulin binding. However, at each age and body weight, cells from the obese, relative to the lean, animals are larger, and their basal and insulin-stimulated rates of glucose transport and metabolism are greater. Insulin binding, on the other hand, starts higher, but decreases with increasing animal age to the level observed in the control cells before increasing again. In this model of obesity, therefore, net adipose cell function reflects the composite effects of multiple, not as yet specifically identified, factors comprising animal age, adipose cell size, and genetic obesity.